<template>
  <div>
    <ul class="list">
      <li class="item" v-for="item of letters" :key='item.id'
        :ref="item"
        @click="handerClick"
        @touchstart.prevent='handleTouchStart'
        @touchmove="handleTouchMove"
        @touchend="handTouchEnd"
      >{{item}}</li>
      
    </ul>
  </div>
</template>

<script>
  export default {
    name:'CityAlphabet',
    props:{
      cities:Object
    },
    data() {
      return {
        touchStatus:false,
        startY:0,
        timer:null
      }
    },
    updated() {
      this.startY=this.$refs['A'][0].offsetTop
    },
    computed: {
      letters(){
        const letters=[]
        for (const i in this.cities) {
          letters.push(i)
        }
        return letters
      }
    },
    methods: {
      handerClick(e){
        this.$emit('change',e.target.innerText)
        //console.log(e.target.innerText);
        //console.log('dddd');
      },
      handleTouchStart(){
        this.touchStatus=true
      },
      handleTouchMove(e){
        if (this.touchStatus) {
          if (this.timer) {
            clearTimeout(this.timer)
          }
          this.timer=setTimeout(() => {
              
            //const startY=this.$refs['A'][0].offsetTop
            const touchY=e.touches[0].clientY-79
            const index=Math.floor((touchY-this.startY)/20)
            //console.log(touchY);
            //console.log(index);
            if (index>=0&&index<this.letters.length) {
              this.$emit('change',this.letters[index])
            }
          }, 16);
        }
      },
      handTouchEnd(){
        this.touchStatus=false
      }
    },
  }
</script>

<style lang="stylus" scoped>
  .list
    display flex
    flex-direction column
    justify-content center
    position absolute
    top 1.58rem
    right 0
    bottom 0
    width .4rem
    .item
      line-height .44rem
      text-align center
      color #00bcd4
</style>